全文获取类型
收费全文 | 10863篇 |
免费 | 587篇 |
国内免费 | 2541篇 |
专业分类
化学 | 12920篇 |
晶体学 | 101篇 |
力学 | 40篇 |
综合类 | 120篇 |
数学 | 95篇 |
物理学 | 715篇 |
出版年
2024年 | 19篇 |
2023年 | 176篇 |
2022年 | 1015篇 |
2021年 | 780篇 |
2020年 | 681篇 |
2019年 | 554篇 |
2018年 | 501篇 |
2017年 | 475篇 |
2016年 | 617篇 |
2015年 | 550篇 |
2014年 | 512篇 |
2013年 | 1002篇 |
2012年 | 791篇 |
2011年 | 609篇 |
2010年 | 413篇 |
2009年 | 566篇 |
2008年 | 547篇 |
2007年 | 542篇 |
2006年 | 453篇 |
2005年 | 394篇 |
2004年 | 346篇 |
2003年 | 298篇 |
2002年 | 476篇 |
2001年 | 183篇 |
2000年 | 202篇 |
1999年 | 190篇 |
1998年 | 164篇 |
1997年 | 130篇 |
1996年 | 118篇 |
1995年 | 113篇 |
1994年 | 98篇 |
1993年 | 77篇 |
1992年 | 64篇 |
1991年 | 62篇 |
1990年 | 37篇 |
1989年 | 61篇 |
1988年 | 40篇 |
1987年 | 14篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 17篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We have synthesized a new series of azo‐bis antipyrine derivatives from a one‐pot multicomponent Knoevenagel/Michael addition reaction of antipyrine, with a diversity of azo aldehydes in ethanol and L‐Proline as a catalyst under reflux condition. The anti‐inflammatory activity of the final products was assessed using the inhibition of albumin denaturation technique. Compound 3f showed an inhibitory effect with IC50 values of 3.6 μM with respect to the standard anti‐inflammatory drug Aspirin, with IC50 values of 2 μM. In addition, molecular docking was performed to confirm the in vitro results against the enzymatic inhibition activity of COX‐2 enzymes in which compound 3f showed good binding affinity with an inhibition constant (Ki) of 1.79 nM. 相似文献
992.
In this brief review, an overview about recent efforts to simulate the spectroscopic signatures of chiral molecules is given with focus on real time propagation approaches to solve the time-dependent Schrödinger equation. In particular the simulation of electric circular dichroism spectra and vibrational Raman optical activity is discussed. In comparison to linear absorption spectra, where only the response of the electric dipole moment is necessary, the response of the magnetic dipole moment and electric quadrupole moment is more intricate. Issues such as gauge origin dependence, basis set dependence, non-local potentials and the dipole approximation are addressed. 相似文献
993.
《印度化学会志》2021,98(3):100027
The convenient route for the synthesis of a series of new Isoindoline-1, 3-dione/phthalimide analogues by condensation of substituted phthalic anhydride with an appropriate Ar-amine is described. Selective phthalimide derivatives were evaluated for their preliminary biological activities against Gram-positive, Gram-negative and fungi strains. These encouraging results could be helpful for the development of new antibacterial or antifungal agents. 相似文献
994.
《印度化学会志》2021,98(3):100033
The simple and more reliable one-pot synthesis of some novel compounds of allyl/Benzyl quinazolinone (4aa-4bd) with good yields from readily available derivatives of anthranilic acid and benzoyl chloride was also reported. Interestingly, as compared to Diclofenac sodium, compounds 4ac, 4ad, 4ba, 4bc and 4bd displayed remarkable anti-inflammatory activity (Scheme 1 & Table 2). 相似文献
995.
以2,3-二氨基吡啶和2,3-丁二酮为起始原料,经环化、催化氢化和亲核取代反应合成了10个新型哌啶并[2,3-b]哌嗪类衍生物(3a~3j),其结构经1H NMR、13C NMR和HR-MS确证。体外抗血小板聚集活性研究表明,化合物3d、3e、3g、3h和3j具有一定的抗血小板聚集作用,其中化合物3h(IC50=1.24mmol/L)的活性显著优于母体化合物川芎嗪(IC50=3.96mmol/L)和阳性药物阿司匹林(IC50=2.41mmol/L)。 相似文献
996.
合成了3种含姜黄素衍生物(L1~L3)和1,3,5-三氮杂-7-磷金刚烷(PTA)配体的芳基钌配合物[(η6-p-cymene)Ru(L)(PTA)]PF6(1~3,L=L1~L3),通过X射线单晶衍射、核磁共振波谱、高分辨质谱、元素分析等方法表征了这些配合物的结构,并用MTT法研究了它们在λ>400 nm的光照辅助下对Hep G2人肝癌细胞的增殖抑制活性。结果表明,这3个配合物均为半三明治型结构;光辅助下,配合物抗癌活性明显提高,其中配合物3对HepG2细胞的IC50值从(60.3±1.1)μmol·L-1降低至(45.0±6.1)μmol·L-1。说明光照可以有效提高此类配合物的抗肿瘤活性。 相似文献
997.
Rui P. Queirós Daniel Rainho Mauro D. Santos Liliana G. Fidalgo Ivonne Delgadillo 《高压研究》2015,35(1):69-77
This study evaluated high pressure processing (P1 – 400?MPa/5?min; P2 – 550?MPa/2?min) and thermal pasteurization (TP – 70°C/30?s) effects on sweet cherry juice's microbiological and physicochemical parameters, during four weeks of refrigerated storage. All treatments reduced the microbiological load to undetectable levels not affecting total soluble solids and titratable acidity. The pH increased with all treatments, however, it decreased during storage. Phenols were differently affected: TP increased them by 6%, P1 had no effect while P2 decreased them by 11%. During storage, phenols in control and TP samples decreased by 26% and 20%, P1 samples decreased them by 11% whereas P2 showed no variation. TP had no effect on anthocyanins, while pressure treatments increased them by 8%. Anthocyanins decreased during storage, particularly in the control and P1 (decreasing 41%). All treatments had no effect on antioxidant activity until the 14th day, thereafter high pressure processing samples showed the highest antioxidant activity. 相似文献
998.
Experiments by F. Zhou and coworkers (2010) [16] showed that mitochondria are the main target of the cellular accumulation of single-walled carbon nanotubes (SWCNTs). Our in silico experiments, based on geometrical optimization of the system consisting of SWCNT+proton within Density Functional Theory, revealed that protons can bind to the outer side of SWCNT so generating a positive charge. Calculation results allow one to propose the following mechanism of SWCNTs mitochondrial targeting. SWCNTs enter the space between inner and outer membranes of mitochondria, where the excess of protons has been formed by diffusion. In this compartment SWCNTs are loaded with protons and acquire positive charges distributed over their surface. Protonation of hydrophobic SWCNTs can also be carried out within the mitochondrial membrane through interaction with the protonated ubiquinone. Such “charge loaded” particles can be transferred as “Sculachev ions” through the inner membrane of the mitochondria due to the potential difference generated by the inner membrane. Physiological consequences of the described mechanism are discussed. 相似文献
999.
The sweep frequency ultrasound (SFU) and single frequency countercurrent ultrasound (SFCU) pretreatments were modeled and compared based on production of angiotensin I-converting enzyme (ACE) inhibitory peptides from garlic hydrolysates. Two mathematical models were developed to show the effect of each variable and their combinatorial interactions on ACE inhibitory activity. The optimum levels of the parameters in SFU were determined using uniform design, which revealed these as follows: total ultrasonic time 1.5 h, on-time of pulse 18 s and off-time of pulse 3 s. Under optimized conditions, the experimental values of SFU and SFCU were 65.88% and 67.78%, which agreed closely with the predicted values of 63.44% and 67.33%. The SFU and SFCU pretreatments both resulted in higher ACE inhibitory activity compared with untreated garlic (p < 0.05). However, there were no significant differences in the ACE inhibitory activities and IC50 values obtained from SFCU and SFU pretreatments under optimum conditions (p > 0.05). 相似文献
1000.
Jiri Ullschmied 《辐射效应与固体损伤》2015,170(4):278-289
The Prague Asterix Laser System (PALS) Research Infrastructure (RI) in Prague, one of only four kJ-class laser facilities in EU, has been offering its beam time to European researchers for already 14 years, since 2004 in the framework of the LASERLAB-Europe consortium. Till June 2014, the PALS RI has provided 4313 experimental days for a total of 41 projects with 303 international users from 42 different research institutions. Its principal experimental facility is a terawatt sub-ns iodine laser (1315?nm) with an optional plasma-based zinc XUV laser (21.2?nm), and an auxiliary Ti:Sapphire fs laser (1?J, 70?fs) exploited for femtosecond plasma probing and experiments with synchronised femtosecond and sub-nanosecond laser pulses at mean laser intensities of up to 30?PW/cm2. The lasers are equipped with several target facilities and rich sets of instruments for both active and passive plasma diagnostics. The PALS main research areas include development and applications of secondary laser sources of high-energy ions and both coherent and non-coherent high-intensity XUV radiation, laboratory astrophysical and inertial fusion-relevant studies. In this paper, the main results having been achieved at PALS in the framework of LASERLAB-EUROPE international access activities during the last four years are highlighted. 相似文献